The present invention relates generally to roadway safety devices and more particularly, to a guardrail beam with enhanced stability.
A goal of roadway safety is to provide a forgiving roadway and adjacent roadside for errant motorists. Guardrails are employed along a roadside to accomplish multiple tasks. Upon vehicle impact, a guardrail must react as a brake and shock absorber to dissipate the kinetic energy of the vehicle. Subsequently, the guardrail acts as a mechanical guide to redirect the vehicle away from hazards during deceleration and to prevent the vehicle from leaving the road, becoming airborne or rebounding into traveled lanes of traffic.
For many years, a standard heavy gauge metal guardrail known as the xe2x80x9cW-beamxe2x80x9d has been used on the nation""s roadways to accomplish these tasks and others. Named after its characteristic shape, the xe2x80x9cW-beamxe2x80x9d is typically anchored to the ground using posts made of metal, wood or a combination of both.
Recently, there has been a vigorous effort to raise the performance standards which guardrails must satisfy. Increasingly stringent testing criteria have uncovered some deficiencies in the performance of standard xe2x80x9cW-beamxe2x80x9d guardrails. Accordingly, recent efforts have focused on the development of a new guardrail system that will accomplish safety goals more effectively.
One such design included a deeper and wider xe2x80x9cW-beam.xe2x80x9d However, this change in geometry required a significant increase in hardware to attach adjacent sections of the beam at each splice. Such alternative systems have not gained widespread industry acceptance because they typically lacked the ability to efficiently interface with existing guardrail systems.
One aspect of the present invention is to provide an improved guardrail system for use in median strips and adjacent to roadways that more evenly spreads the stresses sustained during impact with a vehicle to create a more uniform, stable and predictable response. Another aspect is to provide a cost-effective, retrofitable guardrail which can be employed interchangeably along with, or in lieu of existing guardrail systems. Multiple splice bolt holes or slots associated with each guardrail beam are preferably provided to allow the guardrail beams to be used interchangeably with existing guardrail systems. Yet another aspect is to provide a lightweight guardrail with sufficient strength to meet or surpass highway safety standards. Still another aspect is to provide a guardrail system capable of dissipating the impact energy of a vehicle collision more effectively than existing guardrail systems.
Various technical benefits are attained in accordance with the teachings of the present invention by employing a guardrail beam with a first edge, second edge and a plurality of crowns disposed longitudinally between the first edge and the second edge. A first fold may be disposed longitudinally along the first edge and a second fold may be disposed longitudinally along the second edge. These folds may be integrally formed on a base sheet of steel or other material from which the guardrail beam is manufactured. Alternatively, the desired folds may be added either during manufacture or during installation of the guardrail by bonding, fastening, or welding additional portions as desired to a guardrail beam. For some applications, fold portions incorporating teachings of the present invention may be added to a base sheet prior to manufacturing a guardrail beam. These fold portions may be of constant or of variable thickness, and may for some applications be substantially thicker than the associated base sheet material to maximize the local or overall benefits of the present invention. In some applications twisted or layered fibers or wires may be included to aid in this purpose. For some applications a guardrail beam may be formed in accordance with teachings of the present invention from a base sheet having variable thickness and/or composition to enhance material and/or strength and stiffness redistribution as well as to provide local strengthening and fracture control or management such as for strengthening adjacent to splice bolt slots, or in the interior region to maximize overall crash energy is dissipation.
A guardrail beam incorporating teachings of the present invention may also include for the purpose of describing various embodiments of the invention, an upstream end, a downstream end spaced longitudinally from the upstream end, and an intermediate portion disposed between the upstream end and the downstream end. The first and second folds may form generally tubular first and second curls within the upstream and intermediate portions. Each curl may have an outer diameter with a value between approximately xe2x85x9c of an inch and 2xc2xd inches. For some applications, the first and second folds may be generally hemmed or otherwise modified adjacent to the downstream end to accommodate forming a splice with the upstream end of another guardrail beam.
In a particular embodiment, at least one fluted bead having a radius with a value between approximately 0.125 inches and 0.32 inches may be disposed longitudinally along at least one crown of a guardrail beam formed in accordance with teachings of the present invention. In another embodiment the flutes may be of variable shape and size, or they may be combined with axially oriented strips or fibers of the same or different materials as compared to the base sheet material in order to combine their strengthening and/or energy absorbing effect with or to replace the flutes. The combination may include bonding, fastening, or welding of the strips or fibers on a base sheet or on a guardrail beam after being formed from a base sheet. Such strips or fibers may also be combined with edge folds in a similar fashion. These strips or fibers may resist damage, reinforce, or absorb energy in various ways, such as by being arranged to produce mechanisms for energy absorption, including but not limited to converting kinetic and/or potential energy into heat energy at a microscopic and/or macroscopic level during a vehicle collision. The strips and/or fibers may also serve as safety or cosmetic markings that signal or provide guidance to motorists, such as by light or electronic media.
A technical advantage of the present invention includes its ability to effectively withstand and distribute stresses sustained during impact with a vehicle. This enhanced stress distribution minimizes failure of the guardrail beam and provides for a more stable and predictable response during collision. Accordingly, the resulting guardrail beams can withstand significant forces of impact while maintaining adequate safety to vehicles, passengers, and bystanders.
Another technical advantage includes the use of thinner sheets of selected base sheet materials to form a guardrail beam which minimizes costs associated with fabrication, transportation and installation of the guardrail beam.
Still another technical advantage includes a splice bolt hole or slot configuration which facilitates the retrofit and/or replacement of existing guardrail systems with one or more sections of a guardrail beam formed in accordance with teachings of the present invention without requiring substantial modifications to existing equipment and other portions of each guardrail system.